In IP-based Ethernet networks, voice VLAN is vital to ensure the quality of the voice data transmission. Then, what is it? How does voice VLAN work? What can we benefit from it? Get all the answers to these questions and other FAQs about voice VLAN from this post.

What Is Voice VLAN?

A voice VLAN is a VLAN ( virtual local area network) that is specifically allocated for user's voice data streams. It ensures the quality of voice traffic by improving the transmission priority of it when transmitted with other traffic. That is to say, when other services (data, video, etc.) are transmitted simultaneously, voice service will be prioritized and transmitted with a higher forwarding priority.

How Does Voice VLAN Work?

To increase the priority of the voice data streams, you must first identify them. Voice VLAN can identify voice data streams in two ways: One is by identifying the source MAC addresses of the received packets (MAC address-based mode), and the other is by identifying VLAN tags of the received packets (VLAN-based mode).

In the MAC address-based mode, a network switch can determine whether the data stream is a voice data stream according to a source MAC address field in a data packet that enters its interface. As shown in the picture below, after receiving the packet sent by the PC and the IP phone, the switch performs the following processing: If the source MAC address matches the OUI (Organizationally Unique Identifier) configured on the switch, the tag of the voice VLAN is added to the packet, and the packet priority is increased. If the source MAC address doesn’t match the OUI, the VLAN tag of PVID is added to the packet and the packet won’t be sent with priority.

In the VLAN-based mode, a network switch determines whether the data packet is a voice packet based on the VLAN ID of the packet entering the interface. As shown in the following picture, the IP phone firstly sends packets to a network switch. Then, the switch receives the packets and send them back after adding the voice VLAN information in relevant field s. After receiving the packets carrying voice VLAN information, the IP phone sends the voice packets with tags again. If the tag matches the voice VLAN configured on the switch, the switch forwards the packet priority. In this way, the switch can ensure the priority transmission of voice packets when network congestion occurs.

What Can We Benefit From Voice VLAN?

There are three main advantages of using voice VLAN.

Firstly, it ensures that your VoIP (Voice over Internet Phone) devices do not have to contend directly with all the broadcasts and other traffic from the data VLAN. It can be used for QoS guarantee on IP networks when multiple VLANs are configured and trunked on the uplinks with 802.1Q on a network switch.

Secondly, a voice VLAN can simplify network configuration in some circumstances. It is much easier to mark packets for QoS than specify various ranges of TCP and UDP ports. Similarly, TFTP and the special DHCP services for VoIP phones are easier to configure when all VoIP phones are in the same subnet.

Thirdly, a voice VLAN can be used to prioritize different voice services since it supports 802.1p Class of Service (CoS) priority or DSCP (Differentiated Services Code Point) priority.

Confusing Questions About Voice VLAN

1. How to Configure Voice VLAN?

According to the voice VLAN principles above, there are two modes for voice VLAN configuration.

In the MAC address-based mode, there are three main steps to configure voice VLAN:

1. Create a VLAN on the switch and add interfaces to the VLAN to implement Layer 2 interworking.

2. Configure the OUI to match the source MAC address of the received packet.

3. Configure the voice VLAN function on the interface.

In the MAC address-based mode, there are two main steps to configure voice VLAN:

1. Create a VLAN on the switch and add interfaces to the VLAN to implement Layer 2 interworking.

2. Configure a VLAN as the voice VLAN and use the VLAN-based voice VLAN.

For more details, just refer to Voice VLAN Configuration on FS S3900 Series Switches.

2. What Are Applicable Scenarios of Voice VLAN?

Voice VLAN is generally used in scenarios where IP phones exist such as big enterprises and financial industries. In these places, offices are widely distributed and the staff is scattered, increasing the need for IP phones to maintain frequent multi-party communication. When there is no need to connect a PC for data services, voice VLAN is typically used in conference rooms.

3. Network Switches That Support Voice VLAN

Not all the network switches support voice VLAN technology. Normally, PoE switches support voice VLAN and can offer power for IP phones, such as FS S1150-8T2F, S3260-8T2FP, S1400-24T4F, etc. Other switches may support voice VLAN but can’t power the IP phones connected to them, such as FS S3900/S5800/S5850 series switches.